A major problem with wiper blade inserts manufactured from soft flexible rubber is that the rubber takes a permanent set during its service life and thereafter does not wipe properly. A wiper blade that is functioning properly flips over at the beginning of each stroke; thereby, the blade always wipes with the square cut end or lip of the blade trailing the wiper blade carrier arm. The large number of patent applications purporting to solve the problems of ineffective windshield wiping are evidence of the continuing search for a better solution.
At least five of the problems that we have identified with present wiper blade technology may be solved by the present invention. These problems are: 1) permanent set of the wiper blade; 2) slow elastic response of the blade; 3) ozone degradation; 4) solvent degradation; and 5) ultraviolet radiation degradation.
The permanent set reduces the blade's ability to return to its exact original position and prevents the blade from rapidly flipping, resulting in an unsatisfactory wipe. The permanent set occurs because the wiper blade is pressed against the windshield under the necessary pressure of the wiper blade carrier arm. When the blade is in this flexed position for a prolonged period at temperatures ranging from about -30.degree. C. to about +130.degree. C. with exposure to sunlight, ozone, rain water, salt water, acid rain, solvents in windshield wiper fluid, etc., the permanent set occurs along the relatively thin shank portion of the blade. Of particular interest are the solvents encountered in windshield wiper fluids and/or automotive environments that cause swelling of rubber, either natural or synthetic.
Another factor influencing wiper performance is the slow elastic response of a rubber of the type suitable as a wiping surface. In compounding a rubber that is suitable as a wiper blade, the rubber compounder necessarily compromises rubber properties to adjust the wiping capability and the elastic response, frequently with the preference being given to wiping capability,
As described further below, the present invention seeks to solve these problems.